The incidence of microbial infections (e.g., mycobacterial, fungal, and protozoal infections) in the immunocompromised population has significantly increased over the past several years. In particular, Candida species, especially Candida albicans, are often significant pathogens in patients infected with human immunodeficiency virus (HIV). Another pathogen, Pneumocystis carinii, causes a form of pneumonia (PCP) that is believed to be one of the leading causes of death in patients suffering from AIDS.
In addition, human African trypanosomiasis (HAT) has reemerged as a threat to over 60 million people. Current estimates are that between 350,000 and 450,000 people are infected with HAT. Other severe and life-threatening microbial infections are caused by Plasmodium spp., Mycobacterium tuberculosis, Aspergillus spp., Cryptosporidium parvum, Giardia lamblia, Toxoplasma gondii, Fusarium solani, and Cryptococcus neoformans. 
The antimicrobial properties of dicationic molecules have been studied since the 1930's. Compounds of this type have typically utilized amidine groups as the cationic moieties, and their activities against a number of pathogens including Trypanosoma spp., Plasmodium spp., Cryptosporidium parvum, Giardia lamblia, Leishmania spp., Pneumocystis carinii, Toxoplasma gondii, Candida albicans, Aspergillus spp. and Cryptococcus neoformans have been reported. See, e.g., King, H., et al., Ann. Trop. Med. Parasitol., 32, 177-192 (1938); Blagburn, B. L., et al., Antimicrob. Agents Chemother., 35, 1520-1523 (1991); Bell, C. A., et al., Antimicrob. Agents Chemother., 35, 1099-1107 (1991); Bell, C. A., et al., Antimicrob. Agents Chemother., 34, 1381-1386 (1990); Kirk, R., et al., Ann. Trop. Med. Parastiol., 34, 181-197 (1940); Fulton, J. D., Ann. Trop. Med. Parasitol., 34, 53-66 (1940); Ivady. V. G., et al., Monatschr. Kinderheilkd., 106, 10-14 (1958); Boykin, D. W., et al., J. Med. Chem., 38, 912-916 (1995); Boykin, D. W., et al., J. Med. Chem., 41, 124-129 (1998); Francesconi, I., et al., J. Med. Chem., 42, 2260-2265 (1999); Lindsay, D. S., et al., Antimicrob. Agents Chemother., 35, 1914-1916 (1991); Lourie, E. M., et al., Ann. Trop. Med. Parasitol., 33, 289-304 (1939); Lourie, E. M., et al., Ann. Trop. Med. Parasitol., 33, 305-312 (1939); Das, B. P., et al., J. Med. Chem., 20, 531-536 (1976); Del Poeta, M., et al., J. Antimicrob. Chemother., 44, 223-228 (1999); Del Poeta, M., et al., Antimicrob. Agents Chemother., 42, 2495-2502 (1998); Del Poeta, M., et al., Antimicrob. Agents Chemother., 42, 2503-2510 (1998).
Despite the broad-spectrum of antimicrobial activity exhibited by aromatic diamidines, only one compound of this chemical type, pentamidine, has seen significant clinical use in humans. See Tidwell R. R. and Boykin D. W., Dicationic DNA Minor Groove Binders as Antimicrobial Agents, in Small Molecule DNA and RNA Binders: From Synthesis to Nucleic Acid Complexes, (Demeunynck, M.; Bailly, C. and Wilson, W. D. (eds.) Wiley-VCH, New York), Vol. 2, pp 414-460 (2003). Pentamidine has been used clinically against African trypanosomiasis, antimony-resistant leishmaniasis, and P. carinii pneumonia. See, e.g., Apted, F. I. C., Pharmacol. Ther., 11, 391-413 (1980); Bryceson, A. D. M., et al., Trans. Roy. Soc. Trop. Med. Hyg., 79, 705-714 (1985); Hughes, W. T., et al., Antimicrob. Agents Chemother., 5, 289-293 (1974). Thus, there continues to be a need for improvement in the art for additional compounds having desirable antimicrobial activity, whether against the representative pathogens referenced above or against other pathogens.